Acoustic diaphragm



Feb. 26., 1924. 1,484,820

H. DUNCAN ACOUSTIC DIAPHRAGM Filed March :1, 1919 a vwewto c PatentedFeb. 26, 1924.

ATENT-cranes.

HARRY L.' DUNCAN, F MAHWAH, NEW JERSEY.

ACOUSTIC DIAPHRAGM.

Application filed March 31. 1919. Serial No. 286,351.

To all whom'it may concern: Be it known that I, HARRY L. DUNCAN, acitizen of the United States, and resident of Mahwah, county of Bergen,State of New 6 Jersey, have made a certain new and useful InventionRelating to Acoustic Diaphragms, of which the followin -is aspecification, taken in connection with the accompanying drawing.-

This invention relates especially to acous tic dia hragms forphonographs, telephones and 0t er urposes in which the metallic or otherdiap ragm is formed with a wavy or fluted edge so that-the edge may begiven a definite degree of peripheral elongation.

The diaphragm may be clamped or mounted in such a way that thisirregular or fluted edge is forced more or less into the flat orstraight position so that in this way the edge diameter of the diaphragmtends to enlarge which automatically places the central portions of thedia hragm under radial tension and increases tlie pitch or efliciency ofthe diaphragm for many -pur oses. In the case of metal diaphragmstiiecentral portion of the diaphragm may in many cases be advantageouslystiffened by bein coned u or corrugated at the same time t at the e geportion of the diaphragm is given a fluted or wavy shape in suitabledies or other forming tools, and if desired, an edge tensioning ring ormember of suitable wavy or fluted, form may in some cases be.advantageously more or less enclosed within or united to the edgeportion of the diaphragm and sufficiently flattened in the mounting orsubsequent use of the diaphragm so' as to place the portions of thediaphragm within under suitable radial tension. Such dia- 40 phragms maybe made of any suitable material and steel or other sheet metal such asbrass, bronze or aluminum alloys ma be used in some cases or plastic ormoul able material may be used for this purpose, such as celluloid orrubber with or without such unitedv or enclosed metal "tensioning mem-'bers, or fibrous materials .may be used in many cases, and also paper,paper pulp or cloth which may in some cases be advantageouslyimpregnated or coated with cementing material of various kinds, such,for example, as phenolic condensation compositions like bakelite varnishwhich under theheat curing treatment stifien the fabric'or phragmmounted.

Figs. 3 and 4 are similar sectional views showing other forms ofdiaphragm.

Fig. 5 is a sectional view showing the edge drawing or fluting of ametallic diaphragm; and

v Fig. 6 shows the diaphragm which may be produced in this way.

Many types of acoustic diaphragms may advantageously be provided withfluted or sinusoidal edge tensioning members formed integral with orsecured to the diaphragm so as to have a substantially definite degreeof extra peripheral elon ationp When the diaphragms are mounte for useor prior thereto, this edge tensioning member may be more or lessflattened 0r straightened so as to have sufficient increased diameter toexert a valuable radial tensioning action on the inner portions of thediaphragm which may either be substantially flat or given any otherdesired or suitable shape as by stiff-- ening corrugations orprojections in some cases. The edge tensioning device naturally has suchstrength and size as is suited to the size of the diaphragm and forspecial large diaphragms of six inches or more in diameter heavier edgetensioning members are naturally necessary to properly tension theheavier and thicker diaphragms used under such conditions. In lar e iaphragms it is usuall desirable to ave a greater number of e ge flutes orwaves to accommodate the added peripheral length of the tensioningmember before it has exerted its, tensioning action. For smalldiahragms, such 318. 336 more generally used or phonograph andsimilarpurposes and where the diaphragm is only two or thm inches or soin diameter, thinner and lighter material is usually. desirable for thediaphragm body, and where sheet steel is used for this purpose it mayadvantageously be given a more uniform structure and elasticity indifferent directions by special rollmg or preliminary treatment,including cross-rolling or" the plates. Thesteel should of course haveas uniform thickness as possible and a good light diaphragm of thischaracter may be three to ten thousandths of an inch or so thick andhave such composition as is suited to the particular use of thediaphragm, depending, of course, on whether it is to have magneticproperties or not. In some cases it is advantageous to have thediaphragm center stifi'ened so as to get more uniform action inconnection with the operating mechanism connected therewith and asindicated in Fig. 1 the diaphragm l of such sheet metal, for instance,may have its center 3 coned or dished up in such form as to givesuitable stiflness at the same time that the edge portions of thediaphragm are given a fluted or wavy form in the stamping or shapingdevices. For many purposes it is desirable to simultaneously forcetogether the diaphragm and edge tensioning member which may be usedtherewith in some cases, and an edge tensioning ring which is ofconsiderably thicker sheet metal than the diaphragm is shown in Fig. 1and may have four to six times as great thickness as the diaphragm andmay have a radial width much greater than its thickness. as isindicated. Ample radial strength and stiffness may thus be securedcombined with the facility of bending transversely to the plane of thediaphragm in fluting or straightening the ring. It is sometimesdesirable to have the tensioning ring or member 6 arranged in thestamping die when the diaphragm is shaped up and its edge fluted with orwithout coning or stiffening of the center portion and in such case thediaphragm edge may be flanged down around the tensioning ring so as toform a flange 4, a subsequent spinning or shaping operation beingresorted to if desired to force the extremeedge 5 of this diaphragmaround the other side of the stiff ening ring which is thus more or lessenclosed by the diaphragm edge. The part 2 of the diaphragm edge isshown as somewhat separated from the tensioning ring 6 for greaterclearness. although it is of course understood that these parts will beforced closely and tightly together at the same time that the diaphragmedge and tensioning ring are fluted or corrugated to the desiredextentwhich for small diaphragms may mean a difference of a sixteenth toan eighth of an inch or so between the planes of the high points, suchas 2, and the low points, such as 12.- of the diaphragm edge which mayhave four to six or more flutes therein. With metal diaphragms it isusually desirable to definitely secure the diaphragm edge to anytensioning ring or member that may be used, and for this purpose thediaphragm edge and tensioning ring may be soldered, welded or otherwiseunited while still in their fluted or wavy form and for this purposethey maybe clamped together in any desired way after the tensioningmember and flat or other diaphragm have been edge fluted and in somecases annealed to relieve local stresses and then spot welded atsuitable intervals or soldered together by various solderingcompositions depending on the materials used.

Such a diaphragm may be mounted in a clamping support such as isindicated diagrammatically in Fig. 2 as comprising two clamping membersor rings 9, 10 between which the edge portions of the diaphragm may beclamped, suitable 'ashers or cushioning members such as 8 of yieldingmaterial being preferably interposed and for this purpose relativelysoft fibrous material, such as soft paper or rubber sheeting or thelike, may be employed and having sutficient thickness so that thediaphragm edge is firmly engaged throughout its entire periphery-bythese clamping or supporting washers. The clamping members arepreferably brought together to such an extent as to straighten the wavyor fluted edge portion of the diaphragm sufficiently to secure theradial tensioning desired in the diaphragm body and a considerableincrease of pitch can be secured in this way as well as more definiteand desirable results for many classes of acoustic work.

Fig. 3 shows a form of diaphragm which may, if desired, be made ofsubstantially uniform thickness throughout the edge portions andadjacent inner portions of the diaphragm, the desired fluted or wavycharacter of the diaphragm edge being secured by any suitable methoddepending on the diaphragm material employed. A thin sheet metaldiaphragm 1 may be stamped or forced into the desired shape at the sametime that the diaphragm center 3 is forced out into more or less conicalprojecting position which stitfens this part of the diaphragm. The edgeportions 14, 15 may be given a fluted or wavy character and may have ahalf a dozen or more edge flutes such as 14, 15 in which there is adifference of a sixteenth of an inch more or less between the planes ofthe high and low points in small diaphragms a couple of inches indiameter, this amount of edge fluting depending somewhat on the intendeduses of the diaphragm. If desired. however, a diaphragm of this generalcharacter with or without corrugated or conically reenforced centerportions may in many cases be made 'of celluloid or various rubbercompositions,

the degree of edge fluting and the thickness of the diaphragm at variouspoints being of course regulated by the characteristics of the materialemployed in each case as well as the uses for which it is intended. Adesirable material for many forms of diajecting phragm is cloth or otherfibrous material coated and preferably more or lessthoroughly-impregnated with phenolic condensation cementing com ositionssuch as bakelite, redmanol or con ensite varnish, several sheets of softthin and strong paper or fine textured cotton or other cloth beingdesirable. Several Sheets of thin muslin or other cotton fabric which"has been thoroughly impregnated with bakelite varnish or similar pienolic condensation cementing material and dried may be cutapproximately to size and then assembled in a heated mold which canreadily heat the material tov a suflicient extent to render it soft andpliable after which it may be shaped under high pressure and at theproper curing heat for the cementing material employed which for suchbakelite compositions is ap roximately 300to 320 Fahrenheit or so or acurin time of ten or twenty minutes. When suc material is united at thehigh pressure of a number of hundred pounds per square inch thedifferent layers are permanently united b the incorporated curedcementing material so that the'cured diaphragm substantially retains theshape given to it during the molding operation and in this wa a flutedor wavy tensionin edge ma be efinitely formed of such c aracter t atwhen. partially flattened between rubber or other yielding clampingmembers a desirable tension may be given to the central part of thediaphragm which may in some cases be simultaneously formed intoreenforced proosition during the molding operation. 1g. l-shows anotherform of diaphragm may be made of such material and may have four to sixor more edge flutes or wavy portions, such as 14, 15, connected with asuitably reenforced or stifl'ened dia- A: ghragm center of an desiredcharacter. If

esired, such a sti ened center may comprise a series of corrugations 17,18, 19, the center 16 being flat if desired and stiffened in other waysunder some conditions. The Fig. 4 diaphragm may, however, be formed ofsteel or other metal in many cases and the flat diaphragm center 16 mayunder these conditions be advantageous for cooperation with magneticactuating or other members which do not need to be given special shapein order to cooperate pro erly therewith.

In some cases the edge utes or peripheral elongation of a diaphragm maybe formed in other ways, as for instance, by edge drawing rolls such asare diagrammatically indicated in Fig. 5. The two sets of rolls of thischaracter, such as 22, 23, may be arranged on shafts 24 and one or bothsets positively rotated so that a sheetmetal diaphragm 20 arrangedbetween these three or four pairs of conical fluting rolls may besubjected to a compressing and drawing operation at each pass betweenthe rolls so that its peripheral portion may be drawn out or elongatedto the desired extent as determined b the length of this rollingtreatment and t e ressure and conditions thereof. The diap ragm 20 aftersuch an edge rolling or flutin treatment is preferably stamped in suitale dies to give more definite shape to the edge flutes 21', 25, whichmay thereafter be employed for tensioning the inner portions of thediaphragm by clamping them between relativel flat clamping or supportingsurfaces. his flattens the fluted or wavy edge portions sufiiciently sothat they can exert a desirable tension: ing action on the centralportions of the diaphra m which is of greater efiiciency because 0 thehardening and strengthening] ofthe metal during the ed e fluting'rollingoperation to which it has een subjected.

This invention has been disclosed in connection with a number ofillustrative embodiments, forms, proportions, elements,

parts, shapes, materials, compositions, conditions, and methods ofpreparation, production and use, to the details of which disclosure theinvention is not of course to be limited, since what is claimed as newand what is desired to be secured by Letters Patent is set forth in theappended claims:

1. The acoustic diaphragm havin a stiffened center and edge portions, ana metallic fluted edge tensionlng ring having four to six flutes tosecure increased peripheral elongation and enclosed by and secured tothe edge portion of said diaphragm, so that said tensioning ring may beflattened in the diaphragm supporting devices to radially tension theinner central portions of the diaphragm.

2. The acoustic diaphragm having a metal lic fluted edge tensioning ringenclosed by and secured to the edge portion of said diaphragm, so thatsaid tensioning ring may be flattened to radially tension the innercentral portions of the diaphragm.

3. The acoustic diaphragm having a metallic fluted edge tensioning ringsecured to the edge portion of said diaphragm and adapted to have itsfluted portions flattened to radially tension the inner central portionsof the diaphragm.

4. The acoustic diaphragm having a flat sectioned metallic edgetensioning member having three or more flutes and enclosed within andsecured to the edge portion of said diaphragm and adapted to'beflattened in the diaphragm supporting devices to radially tension theinner central portions of the diaphragm.

5. The acoustic diaphragm having a wavy tensioning member secured to theouter portion of saiddiaphragm and adapted to be flattened in thediaphragm supporting devices to radially tension the inner portions ofthe diaphragm.

6. The acoustic diaphragm comprising a stifiened center and edgeportions having a fluted form to secure substantially definite increasedperipheral elongation and adapted to be flattened in the diaphragmsupporting devices to radially tension the inner portions of thediaphragm.

7. The acoustic diaphragm comprising outer portions having a Wavy formto secure substantially definite increased elongation and adapted to beflattened to radially tension inner portions of the diaphragm.

8. The acoustic diaphragm comprising outer portions which have beenflattened from a fluted form comprising three or more flutes to impartsubstantially definite radical tension to inner portions of thediaphragm.

9. The acoustic diaphragm comprising outer portions which have beendistorted from a'substantially definite wavy form to impart radialtension to inner portions of the diaphragm.

10. The acoustic diaphragm having a flattened Wavy tensioning membersecured to the outer portion of said diaphragm and imparting radialtension to inner portions of the diaphragm.

HARRY L. DUNCAN.

